1. Field of the Invention
The present invention relates to a liquid crystal display provided with both reflection and transmission functions which display is used in various office automation (OA) equipment such as a word processor and a personal computer, mobile information terminals such as a mobile telephone device and a PDA (Personal Digital Assistant), or camcorders equipped with a liquid crystal monitor.
2. Background Information
In recent years, a liquid crystal display has been increasingly expected to expand its market to that of a display for portable information terminal devices where the liquid crystal display can make the best use of its peculiar characteristics, i.e., thin in size and light in weight.
Since a mobile information terminal is generally battery-driven, it is important to reduce its electricity consumption. Therefore, attention has been given particularly on reflection type liquid crystal displays which are free of or need not use all the time an electricity-consuming back light and which can achieve reductions in electricity consumption, thickness, and weight.
Displaying modes used in a reflection type liquid crystal display are those widely used in a transmission type such as TN (twisted nematic) and STN (super twisted nematic) modes. However, even liquid crystal displays of TN and STN modes do not have sufficient display qualities as currently demanded in terms of luminance and contrast and are required to be improved in display qualities such as high luminance and improved contrast. The reflection type liquid crystal display has a drawback that it is extremely deteriorated in visibility when it is used in a dark place, resulting in the decrease in the reflection light to be used for displaying. On the other hand, contrary to this, the transmission type liquid crystal display has a problem that it is deteriorated in visibility when used under bright circumstances such as fine weather.
Therefore, a transflective liquid crystal display has been developed which combines a transmission display mode and a reflection display mode. However, it has a problem that light leakage occurs in a black display state, resulting in insufficient black level.
The transflective liquid crystal display requires light to be incident on the liquid crystal layer through a region with a transmission function in the transmission mode. Therefore, it is necessary to dispose a polarizer and one or more polymeric stretched films, typically polycarbonates, between the liquid crystal layer and the back light. However, the liquid crystal display in the transmission mode can not essentially avoid problems regarding viewing angle where the refractive index anisotropy peculiar to the liquid crystal molecules changes the displaying color and reduces the displaying contrast, when viewing the display from an oblique direction, and it is essentially difficult for such a combination of polymeric stretched films and a polarizer to enlarge the viewing angle.
An object of the present invention is to provide a transflective liquid crystal display which is bright in the transmission mode, high in contrast, and less dependent on the viewing angle.